Each one of your items on your list deserves its own discussion. The big plus to your list was already mentioned: helmet. You're asking if you really need all this stuff. It depends on how long you want to keep riding. I think your real question is not these litems per se. Its the commitment on an activity and how it hits your wallet.
So then it becomes a cost/benefit thing. Running is cheaper, a few pairs of shoes per year, good socks, clothing that doesn't really do much in comparision to cycling. Running can be expensive, as you say...injuries which leads to medical costs and unpaid sick leave and the stress of going back to work knowing that there's a ton of work waiting for you.
Now the intrinsic thing. Is biking more fun than running? Go to the Triathlon section and ask those guys what they think, what's more fun, not what's their best event. For me, its more fun than running. In my specific case, I was an ok distance runner because of my power to weight advantage. As I got older that advantage disappeared and I became just an average runner with the threat of kneee problems...a la Dr. Kerlan the Laker's orthopod (at that time...I'm old).
On other thing. The more you ride, the more you like it. For me, I stay off the streets as much as possible and my local area allows me this luxury. Others don't.